This invention relates to a process for producing tetraalkylsilanes, and in particular to a process for producing mixed alkylsilanes.
In recent years, many fluid development programs have been directed toward providing base fluids for use in a variety of high temperature aerospace applications, such as jet engine oils, greases and hydraulic fluids. In applications, such as greases and jet engine oils, where oxidative stability at elevated temperatures is essential, most attention has been directed to perfluorinated fluids and modified polyphenyl ether fluids. Hydraulic fluids are not expected to operate in oxidative environments; therefore, the main areas of concern for hydraulic fluids are thermal stability and hydrolytic stability.
For certain environments, hydraulic fluids must be stable over a wide temperature range. For several years, a highly refined deep dewaxed paraffinic mineral oil has been employed as the base stock for hydraulic fluids having a service range of -40.degree. to +550.degree. F. As operating temperature requirements become more demanding, such as a requirement for an operating temperature range of -65.degree. to +600.degree. F., other materials have been investigated as potential replacements for this mineral oil base stock, because the latter does not have adequate viscosity-temperature properties to provide a hydraulic fluid capable of meeting the viscosity requirements for a -65.degree. to +600.degree. F. hydraulic fluid.
It has been suggested that the more stringent requirements could be satisfied by synthetic hydrocarbon fluids based on hydrogenated polyalphaolefin oligomers. However, it was found that the oligomers were deficient both in viscosity-temperature properties and in thermal stability. Perfluorinated fluids have also been suggested as replacements for the mineral oil base stocks. These fluids, such as perfluoropolyalkylethers and perfluorinated alkyl ether sym-triazines, have excellent thermal and oxidative stabilities. However, the perfluorinated fluids have disadvantages, the most significant of which include high density, poor bulk modulus, elastomer incompatability, etc. Additionally, there is the disadvantage associated with designing a functional hydraulic system around a new class of fluids. Further, hydraulic fluids are complex formulations of a high quality base stock and several functional, property improving additives such as antiwear agents, antioxidants, rubber swell agents and antifoam additives. While such property improving additives are available for hydrocarbon base stocks, additives for the perfluorinated fluids are not available and must be specially synthesized.
Organosilicon fluids are widely employed as adjuncts or substitutes for hydrocarbon oil base hydraulic fluids. Lincoln et al, U.S. Pat. No. 2,129,281, disclose a lubricant comprising a major proportion of a hydrocarbon oil and a minor proportion of an organic silicon compound such as, for example, tetralauryl silane. Ramsden et al, U.S. Pat. No. 2,872,471, disclose that alkyl silanes make excellent hydraulic fluids, e.g., didecyldidodecyl silane is an excellent hydraulic fluid for uses involving wide variations in temperature. Cook, U.S. Pat. No. 2,962,446, discloses that tetraalkyl silanes, in which the alkyl groups are the same or different, are useful as hydraulic fluids.
Heretofore, the development of mixed alkyl silicon fluids has been stifled by the lack of convenient methods for their preparation. For example, preparation of a compound such as ##STR1## where A, B, C and D are alkyl groups, has proceeded in stepwise fashion. The first step involves the making of an alkyl metallic compound, such as an alkyllithium compound e.g. ALi: EQU ACl+2Li.fwdarw.ALi+LiCl (1)
Step 2 involves reacting the alkyllithium compound with silicon tetrachloride: EQU ALi+SiCl.sub.4 .fwdarw.ASiCl.sub.3 +LiCl (2)
Subsequent steps are as follows: EQU BCl+2Li.fwdarw.BLi+LiCl (3) EQU BLi+ASiCl.sub.3 .fwdarw.ABSiCl.sub.2 +LiCl (4) EQU CCl+2Li.fwdarw.CLi+LiCl (5) EQU CLi+ABSiCl.sub.2 .fwdarw.ABSiCCl+LiCl (6) EQU DCl+2Li.fwdarw.DLi+LiCl (7) EQU DLi+ABSiCCl.fwdarw.ABSiCD+LiCl (8)
We have discovered a simpler process for producing mixed tetraalkylsilanes.
Accordingly, it is an object of the present invention to provide a process for producing mixed alkyl silane fluids.
Other objects and advantages of the present invention will become apparent to those skilled in the art from the following disclosure.